Experimental Investigation on the Sputtering Process for Tantalum Oxynitride Thin Films
Round 1
Reviewer 1 Report
Comments to authors
The manuscript entitled: “Experimental investigation on the sputtering process for tantalum oxynitride thin films”, studies the tantalum oxynitrides films deposited by sputtering under fixed nitrogen (10 sccm) and variable oxygen flow rates (0-4 sccm). Post deposition annealing was carried out in order to transform the amorphous as deposited into crystalline phases.
The aim of this work is to investigate the appropriate range of oxygen flow for preparing crystalline tantalum oxynitride. Furthermore, the suitability of the prepared oxynitride films for methyl orange degradation under solar light radiation, is examined.
There are many works in the literature concerning tantalum oxynitride films preparation by magnetron sputtering process using either post deposition thermal annealing with changing O2 flow rate or without thermal annealing with changing fixed mixture (N2+O2) flow rate during deposition. However, it is the first time to my knowledge that variable oxygen flow rates during sputtering associated with post thermal annealing process are used to prepare high quality crystalline tantalum oxynitride thin films with high photocatalytic efficiency.
Only few minor revision-comments have to be considered in order the manuscript results to be more clear:
- In the line 363 the authors state: “…annealed films deposited between 0.75 and 1.25 sccm have higher efficiency on the degradation of methyl orange. This may be attributed to the sufficient quantity of oxynitrides in the film by the higher O2 supply”. As the results of the Fig. 10 show the annealed film deposited at oxygen flow of 1.25 sccm has the highest efficiency compared to the films deposited at oxygen flows of 0.75 and 1 sccm. However, the Raman and XRD results show that for oxygen flow rate of 1.25 sccm the film belongs to a transient behavior between tantalum oxinitrides and tantalum oxides. So, it is not clear that the highest degradation efficiency of this film is due to sufficient quantity of oxynitrides as the authors claim. In my opinion the high degradation efficiency of this film could be attributed to a higher surface roughness which in turns leads to a high effective surface area and thus an increased photocatalytic activity. It would be useful, the surface morphology of the films deposited under flow rates of 0.75 and 1.25 sccm to be added in the Fig. 4.
- Recently, a comprehensive similar study has been published (doi: 3390/nano9030476) investigating photodegradation efficiency of magnetron sputtered tantalum oxynitride thin films by modifying the partial pressure of the reactive gases mixture (15% O2 + 85% N2) between 0.02 Pa and 0.24 Pa, while keeping the other deposition parameters identical. In my humble opinion, this work is worth discussing in the introduction or photo-degradation test sections.
Based on the above mentioned minor revisions the manuscript can be accepted for publication in Photonics journal.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Authors present a research paper titled “Experimental Investigation on the Sputtering Process for Tantalum Oxynitride Thin Films”. They analyzed the film microstructure and its physical properties as a function of oxygen flow rate. The paper presents interesting results and could be published after considering the following comments:
The introduction should be developed and enhanced.
Authors should clearly illustrate the study originality compared to the previous studies and TaON mentioned references.
Authors should present how did they control the oxygen flow rate accurately?
Thermal annealing: please add the heating and cooling rates.
Considering the low accuracy of the EDS technique for the light elements, could authors use other techniques to measure the chemical composition and obtain reliable values (e.g. XPS,....). What are the values errors ?
Authors should show the films growth morphology (Cross-section SEM images).
Authors should analyze the films roughness.
Authors should give more analyses on microstructure (e.g. crystallite size, ...)
Please correct the figures legends n° 3, 4, 5, 6, 7 and 8. Fig 3 legend should be “XRD patterns of annealed films deposited under different oxygen flow rates.”
How can we explain the high oxygen content with increasing the oxygen flow rate in small quantity?
"...the Raman spectra further echo results found in XRD and EDS." The Ta2O5 is not detected by Raman spectra. Please add explanations.
"...resistivities are measurable only for films deposited under oxygen supply less than 0.5 sccm." Please add explanations.
Author Response
Please refer to the attache file.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper of Li et al. described the effect of oxygen deposition pressure on the properties of TaON. I don't find the paper well structured and connected. Many techniques and measurements are presented but no real relation between the results is given. So each finding is on its own. The authors should try to better correlate the different results maybe writing a new section at the end called Discussion which includes a discussion of all the results presented which can be combined and explained by considering all the characterizations used. In this way a better global picture is given to the reader and a more sound story is created. I don't recommend the paper to be accepted for publications at this stage. Major revisions and complement writing are needed.
Other specific points:
-There is a confusion between annealing conditions and deposition conditions. The authors mention the different annealing oxygen pressure but the oxygen has been changed during deposition and not during annealing according to the table.
-The XRD results are not well explained. In the plots some peaks are not labelled and moreover it seems that a pure oxynitride phase is formed only at 1 sccm O pressure. For pressure below this, there is also the presence of Ta oxide phase separated from the oxynitride but the authors don't mention this. They should comment on this point also in relation to other results.
-I don't see how the author could conclude something about the smoothness of their samples just looking at the SEM planar images where the vertical roughness is not accessible. These images are not really bringing much and they can be put in supplementary materials.
-EDS is not a quantitative techniques to extract atomic compositions expecially considering the oxygen content. XRD are more precise than EDS to indicate the phase and composition except if there is an amorphous component but then this should be mentioned.
-The Raman analysis is obsolete and it is difficult to see which information brings to the paper. A better discussion is needed.
-Resisitivity is measured for films grown at low oxygen pressure. between 0.5 and 1 sccm oxygen is the interesting range where oxynitride is formed but this was not measured. why?
-UV-Vis results are uncorrelated to the rest presented. What is their connection with the other findings?what do they bring to the discussion and to the understanding of the material properties?
-It is concluded that the annealed films deposited between 0.75 and 1.25 sccm have higher efficiency on photo degradation but i don't see that so clearly from the graph. Could they explain better this point?
-Optical band gap analysis is interesting and should be better developed.
Author Response
Please refer to the attached file.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Authors present a research paper titled “Experimental Investigation on the Sputtering Process for Tantalum Oxynitride Thin Films”. They have enhanced some points and it could be published in this form.
Reviewer 3 Report
I am happy with the corrections provided by the authors. The paper can be now accepted for publication. Maybe minor editing can be necessary.
